Author/Authors :
SeiyaHagihara، نويسنده , , NoriyukiMiyazaki، نويسنده ,
Abstract :
Duringsevereaccidentofalightwaterreactor(LWR),thepipingofthereactorcoolingsystemwouldbedamagedwhenthepipingissubjectedtohighinternalpressureandveryhightemperature,resultedfromhightemperaturegasgeneratedinareactorcoreanddecayheatreleasedfromthedepositoffissionproducts.Itisconsideredthat,undersuchacondition,short-termcreepathightemperatureswouldcausethepipingfailure.Fortheevaluationofpipingintegrityunderasevereaccident,amethodtopredictsuchhightemperatureshort-termcreepdeformationshouldbedeveloped,usingacreepconstitutiveequationconsideringtertiarycreep.Inthispaper,thecreepconstitutiveequationincludingtertiarycreepwasappliedtonuclear-gradecold-drawnpipeof316stainlesssteel(SUS316),basedontheisotropicdamagemechanicsproposedbyKachanovandRavotnov.TensilecreeptestdataforthematerialofaSUS316cold-drawnpipewereusedtodeterminethecoefficientsofthecreepconstitutiveequation.Usingtheconstitutiveequationtakingaccountofcreepdamage,finiteelementanalyseswereperformedforthelocalcreepdeformationofthecoolantpipingundertwotypesofconditions;uniformtemperature(isothermalcondition)andtemperaturegradientofcircumferentialdirection(non-isothermalcondition).TheanalyticalresultsshowthatthedamagevariableintegratedintothecreepconstitutiveequationcanpredictthepipefailureinthetestperformedbyJapanAtomicEnergyResearchInstitute,inwhichfailureoccurredfromtheoutsideofthepipewall.
